I know what it feels like to have someone poach deer from your hunting area. It happened to me a few years ago and I was pissed, so I'm not defending poaching or poachers when I say this.
Instead of slashing tires or shooting them out, take their picture with a cell phone camera and a picture of their vehicle and licsense plate.
Road hunters should be dealt with the same. I had a co worker who witnessed someone shoot a deer on a public road from private land, while he was traveling on the road. To make a long story short the people who owned the land on the other side of the road thought he had taken a shot and shot at his pickup. They called the game warden who searched the truck for a bullet hole that they claimed they put in his truck bed. Thing is they didn't even hit the pickup so shooting at vehicles, in my opinion is attempted murder.
Littering or not, with all of the crazy stuff that happens on public land, one shouldn't be pointing firearms at anyone unless you intend to kill them.
